Weather permitting, and depending on successful completion of safety and fire system tests, Caltrans officials say they're "cautiously optimistic" they can open the bore to traffic the weekend of Nov. 16.

"We're very excited at the progress of the project," said Caltrans project spokeswoman Ivy Morrison. "We know motorists will be very excited."

The $417 million project is aimed at easing traffic in off-peak directions for motorists who use the tunnel between Orinda and Oakland, providing two dedicated lanes in each direction at all times. Currently, use of the tunnel's middle bore is based on traffic patterns -- open to westbound drivers in the morning and eastbound commuters in the evening. On weekends, it shifts based on traffic need.

Scene of the Highway 24 exiting the Caldecott Tunnel in Oakland, Calif. photographed on Tuesday, April 30, 2013. (Dan Honda/Bay Area News Group)

"In the long term it will certainly reduce traffic in the off-peak directions," Morrison said. "There's going to be greater predictability."

Caltrans said the project, which broke ground in January 2010, is on schedule and on budget.

Final preparations for the opening will require a temporary weekend closure of two bores to finish work on lane configurations and striping. Once open, Caltrans expects up to six months of additional work on landscaping and road improvements.